ToneMappingAndGammaCorrectionEffect: make unit test work on Windows

Some Qt internals rely on a QCoreApplication being available when
running that test on Windows. Therefore, use QTEST_MAIN instead of
QTEST_APPLESS_MAIN.

Change-Id: Ibb5965aed491973741e94a9fbc840cb08f605203
Reviewed-on: https://kuesa-codereview.kdab.com/c/kuesa/kuesa/+/340
Reviewed-by: Mike Krus <mike.krus@kdab.com>

tests/auto/tonemappingandgammacorrectioneffect/tst_tonemappingandgammacorrectioneffect.cpp

@@ -115,6 +115,6 @@ private Q_SLOTS:
       }
 };
 
-QTEST_APPLESS_MAIN(tst_ToneMappingAndGammaCorrectionEffect)
+QTEST_MAIN(tst_ToneMappingAndGammaCorrectionEffect)
 
 #include "tst_tonemappingandgammacorrectioneffect.moc"